1. Field of the Invention
The invention relates in general to transportation apparatus, and more specifically to passenger conveyors such as escalators and movable walks having a plurality of steps, platforms or pallets.
2. Description of the Prior Art
U.S. Pat. Nos. 3,677,388, 3,682,289 and 3,707,220, all assigned to the same assignee as the present application, disclose new and improved passenger conveyor apparatus, such as escalators, in which the steps are pulled up the incline by a toothed step link. A modular drive unit located in the truss, between the load bearing and return runs, just below the transition between the inclined portion and the upper horizontal portion of the escalator, includes a drive chain which engages the toothed step links on both the upper load bearing run and the lower return run.
The escalator construction disclosed by the hereinbefore mentioned patents includes an endless belt having two sides, each of which are formed by pivotally interconnected, toothed step links. Step axles interconnect the two sides of the endless belt, and the steps are clamped to the step axles. The endless belt and steps are guided through the load bearing and return runs, as well as through the turn-arounds which interconnect the load bearing and return runs, by axle rollers or guide wheels on the ends of the step axles, trailer wheels on the steps, and separate guide tracks for supporting the guide wheels and the trailer wheels.
The escalator construction of the hereinbefore mentioned patents provides many advantages over escalators which utilize a step chain and a top sprocket-drive machine to pull the steps up the incline. One of the most significant advantages is the substantial reduction in load on the working parts. As the length of the rise increases, the load on the parts remains low, with additional modular drives being added to the incline as required. The rigid step links maintain a constant distance between the step axles, and tensioning devices, required with the step chain construction, are not required.
The escalator construction of the hereinbefore mentioned patents, however, requires very close tolerances to be observed during the manufacturing and assembly of the endless belt components, in order to achieve the desired operating smoothness, as well as to meet the necessary vibration and sound levels. The reasons for this have not been completely understood, as the modular drive unit, while mounted in the truss, is isolated from the toothed links via elastomeric rollers. Thus, it would be desirable to be able to manufacture the escalators disclosed in the hereinbefore mentioned patents, and achieve the desired smoothness, vibration level, and sound level, while observing manufacturing and assembly tolerances comparable to the prior art escalator construction which utilizes a step chain.